Santana was the best pitcher in baseball in 2004 & 2006, 2nd best in 2008, top 5 in 2005, three additional All-Star level seasons.
Koufax was the best pitcher in 1963, 2nd to Marichal in 1965-66, top 5 in 1964, two additional All-Star level seasons.
Santana's run of greatness is actually longer than Koufax. Postseason accomplishments are great, but it's still just 57 innings of Koufax's career. BTW - Santana had 20 really great postseason innings in 2004 and 2006 when he was the best pitcher in the league.